In cases where a fuel cell stack structure is installed on a vehicle, the fuel cell stack structure is frequently started up/stopped, thus, the fuel cell stack structure needs to have low-heat capacity. Since a gas flow channel, through which gas is distributed for supply to respective cell space areas provided with simplex cells, performs a function to ensure strength of the stack, a function to ensure a space between adjacent simplex cells and a function to allow each simplex cell to have gastight sealing effect to supply gas to the simplex cell, an area with high-heat capacity is partially formed in an unavoidable fashion.
While starting up the fuel stack structure with such configuration, since temperature of an area with low-heat capacity is rapidly heated than that of an area with high-heat capacity, a temperature difference between the two areas occurs. Due to the temperature difference, the separator and unit cell of the solid electrolyte fuel cell is damaged.
Further, since temperature of a gas flow channel area with high-heat capacity is low, temperature of gas for generating electric power lowers whereby power output also lowers. That is, uneven temperature variations cause irregularities in power output.
Heretofore, for the purpose of addressing defects described above, a method has heretofore been known wherein fuel gas is combusted in a burner to allow high temperature exhaust gas, resulting from combustion, to be admitted to a fuel electrode flow channel for the heating of the same. In this respect, various proposals have heretofore been made to provide a startup method, in which incomplete combustion is caused to take place in the burner to allow fuel gas to have reducing property under which a fuel electrode is maintained to have reducing property, and an electric power generation system that includes a catalytic combustor disposed in an air flow channel inside a cylindrical cell not only to permit high temperature gas to flow into a catalytic combustor but also to allow heat, developed in the catalytic combustor, to be efficiently transferred to cells (as disclosed in Japanese Laid Open Publication Nos. 11-162492 and 2004-119298).